One approach to treating surface waters and other contaminated fluids is to coagulate water-borne contaminants with suitable coagulants such as ferric chloride, poly-aluminum chloride, alum, or other coagulants known in the art. Chemical coagulants change surface charge of contaminants, which reduces the repelling force between the contaminants. As such, the coagulants allow the contaminants to collide and coagulate together into larger flocs. Larger particles can still be formed by adding suitable polymers into the contaminated fluid. The polymers form bridges between the flocs to form large agglomerates. The large agglomerates settle with gravity and may be removed by a clarifier or a filter.
Some treatment processes may include modifying the pH of the contaminated fluid prior to adding the coagulants because some coagulants operate best within a specific pH range. For example, some ferric-based coagulants may operate best at reduced pH levels, which may require adding acids to the contaminated fluid. Other coagulants may operate best at specific alkalinities, which may require adding bicarbonate or acids depending on whether the alkalinity is too low or high. In some cases, the addition of the coagulant itself may affect the pH, and neutralization may be required.
Another approach to treating contaminated fluid uses ion exchange to exchange benign molecules with contaminants of concern. An example is the removal of hexavalent chromium. Once the exchange sites of the ion exchange media is spent, the regeneration of the exchange media creates a large volume of brine containing the contaminants of concern.
As used herein, “contaminated fluid” is a fluid that contains undesirable organic, inorganic products, metals, and possibly microbial cells or other microorganisms. Although contaminants are undesirable in the sense that they are usually toxic when ingested or contacted by humans, the term “undesirable” should not be understood to be restricted to such toxic substances.